hud-service in system monitor is currently using 800 MB of memory. Is this normal? What is it for? Is there a way I can reduce it?
Sadly this is this bug which is being looked at and a fix will hopefully be available soon in the software updates...
You could kill the hud-service in the system monitor and recover all the memory it was using, plus it will restart the service:
killall -9 hud-service